Field of the Invention
The present invention relates to an alignment system and a method for calibrating a position of an optical fiber in a bore of a ferrule, a fiber optic ferrule assembly and a fiber optic connector manufactured by the alignment system and the calibrating method.
Description of the Related Art
A ferrule for a fiber optic connector is a high precision element manufactured by a precise machining technology, and the ferrule is a core component of the fiber optic connector. In prior art, steps of manufacturing the fiber optic connector generally comprises: obtaining a bare fiber by peeling an optical cable and cleaning the bare fiber; inserting the bare fiber through a bore of the ferrule in which gel is prefilled; curing the gel to fix the bare fiber in the bore of the ferrule; and processing the ferrule and the fiber by grinding, polishing, testing, etc., to form a ferrule assembly. A manufacturing error is unavoidable during manufacturing the ferrule assembly. Furthermore, a personal error may occur in size for easily fitting/assembling the ferrule assembly, for example, in order to easily insert the fiber through the bore of the ferrule, the diameter of the bore of the ferrule is formed to be larger than the outer diameter of the fiber, causing a size deviation between the outer diameter of the fiber and the diameter of the bore. Thereby, it is likely to occur various errors in the ferrule assembly, for example, a center axis of the fiber is offset from a center axis of the bore of ferrule, a position of the bore is offset from an ideal position of the bore determined with reference to an indexing feature (for example, an outer cylinder of a single-fiber ferrule or a guide hole of a multi-fiber ferrule). As a result, an actual center axis of the fiber in the bore of the ferrule may be offset from an ideal center axis of the fiber determined with reference to the indexing feature of the ferrule due to these errors, increasing the insertion loss of coupling a pair of fiber optic connectors and decreasing the optical transmission performance of the fiber optic connectors.
A mode field diameter of a single-mode fiber is much less than a mode field diameter of a multi-mode fiber. Generally, the mode field diameter of the single-mode fiber is equal to about ⅕ or ⅙ of the mode field diameter of the multi-mode fiber. Thereby, the alignment accuracy of the single-mode fiber is required to be much higher than that of the multi-mode fiber. Accordingly, the precision of the ferrule for the single-mode fiber optic connector is much higher than that of the ferrule for the multi-mode fiber optic connector.
Accordingly, in prior art, in order to ensure the single-mode fiber optic connector to satisfy with standard precision requirements in this art, it is necessary to use the high precision single-mode ferrule to manufacture the high precision single-mode fiber optic connector, and it is impossible to use the low precision multi-mode ferrule to manufacture the high precision single-mode fiber optic connector. That is, during manufacturing the high precision single-mode fiber optic connector, it is necessary to differentiate the high precision single-mode ferrule and the low precision multi-mode ferrule. Although the single-mode single bore ferrule and the multi-mode single bore ferrule both have the same outer appearance and almost the same in structure, the single-mode single bore ferrule has a much higher precision requirement than that of the multi-mode single bore ferrule. For example, for the single-mode single bore ferrule, the requirement on centricity between the bore of ferrule and the outer cylinder of the ferrule is very high, generally required to reach within 1.5 μm, or even required to less than 1 μm for the single-mode fiber optic connector with an ultralow insertion loss. As a result, the single-mode single bore ferrule has a high cost/price, and it directly causes the cost of the single-mode fiber optic connector very high, especially for the single-mode fiber optic connector with an ultralow insertion loss, the cost of the single-mode single bore ferrule may be times higher than that of the multi-mode single bore ferrule.
The precision requirements on the single-mode single-bore ferrule mainly comprise: a high size precision on the diameter of the bore of the ferrule, a high size precision on the concentricity between the bore and the outer cylinder of the ferrule. Hereafter, it will compare the single-mode single-bore ferrule and the multi-mode single-bore ferrule on following precision requirements.
1) Dimensional tolerance on the outer cylinder of the ferrule.
For the single-mode ferrule, the dimensional tolerance of the outer cylinder of the ferrule is generally required to reach about a range of −0.0005 mm˜0.0005 mm.
For the multi-mode ferrule, the dimensional tolerance of the outer cylinder of the ferrule is generally required to reach about a range of −0.001 mm˜0.001 mm.
2) Dimensional tolerance on the diameter of the bore of the ferrule.
For the single-mode ferrule, the dimensional tolerance of the diameter of the bore of the ferrule is generally required to reach about a range of 0.000˜0.001 mm, or even required to reach about a range of 0.0000˜0.0005 mm for a low insertion loss single-mode ferrule.
For the multi-mode ferrule, the dimensional tolerance of the diameter of the bore of the ferrule is generally required to reach about a range of 0.000˜0.004 mm.
3) Concentricity between the fiber and the outer cylinder of the ferrule.
For the single-mode ferrule, the concentricity between the fiber and the outer cylinder of the ferrule is generally required to reach about 0.001 mm, or even required to reach about 0.0005 mm for a low insertion loss single-mode ferrule.
For the multi-mode ferrule, the concentricity between the fiber and the outer cylinder of the ferrule is generally required to reach about 0.004 mm.
In order to overcome the above problems in the prior art, the applicant of the present invention once proposed a solution in which the high precision single-mode fiber optic connector can be manufactured by using the low precision multi-mode ferrule (with a large bore diameter and a large eccentric), instead of using the expensive high precision single-mode ferrule. The solution simplifies the production, decreases the cost, and improves the optical performance (for example, decreasing the low insertion loss) of the high precision single-mode fiber optic connector.
In the solution provided by the applicant before, the single-mode fiber protruding from the ferrule is introduced into a high precision indexing tool, so that a center of a coating layer on the single-mode fiber is aligned with a center of a high precision alignment bore in the indexing tool. After being aligned, the single-mode fiber is fixed in the bore of the low precision multi-mode ferrule. In this way, a high precision single-mode optic ferrule assembly or connector can be manufactured by using the low precision multi-mode ferrule.
However, this solution is achieved by aligning the center of the coating layer on the fiber, instead of aligning a center of a fiber core of the fiber. Thereby, in this solution, there is a prerequisite that the coating layer and the fiber core of the fiber must have good concentricity. Unfortunately, an eccentric error is unavoidable between the coating layer and the fiber core of the fiber during manufacturing the fiber. The eccentric error is random and cannot be controlled in the practice. For example, different batches of fibers may have different eccentric errors, even the same batch of fibers may have different eccentric errors, and the fibers from different manufactures may have different eccentric errors. Furthermore, there may be contaminants, for example, particles/dusts, attached on the surface of the coating layer of the fiber. As a result, in this solution provided by the applicant before, it cannot ensure that the center of the fiber core of the fiber is aligned in the highest precision. Concerning this, the present invention is proposed.